The present invention generally relates to a system for effectuating automatic gain control of signals which may have a large dynamic range, and more particularly to a system that examines an array of digital signal values to determine the appropriate amount of signal gain based on the range of signal values and the percentage of any signal values from that fall both above and below the bounds of a signal value domain.
Automatic gain control techniques are reluctantly used in underwater hydrophone arrays because of their notorious reputation for oscillatory behavior. The problem of robust gain control in autonomous systems involves balancing efficient use of the information channel against the possible loss of data. For example, a short transient tends to destabilize autonomous systems. Therefore, a need exists for a stable automatic gain control system having a large dynamic range, but which tends to remain at a particular gain setting in the presence of transient signals.
The present invention provides an automatic gain control system that may be implemented in digital hardware. The digital hardware processes an algorithm that determines whether or not to change gain settings. An important feature of the invention is that gain increases are only effectuated if a predetermined time interval has expired after initialization of an interval timer. The digital hardware determines the range of a set of digital data values, and then examines each digital data value in a sequence. An index counter increments a sample count index i each time a new digital data value is examined and determines the absolute value of the ith digital data value. The digital hardware also counts both the number j of digital data values that exceed a high percentage value of the range, and the number k of digital data values that are less than a low percentage value of the range as the digital hardware runs through the sequence. If the digital hardware determines that a digital data value is greater than the high percentage value, the ratio j/i exceeds a first threshold value, and the gain level is not set to the lowest gain level, then the gain is decreased. If the digital hardware determines that a digital data value is less than the low percentage value, the ratio k/i exceeds a second threshold value, a predetermined time interval has elapsed since the initialization of a timer, and the gain level is not set to the highest gain level, then the gain is increased.
An important advantage of the invention is that it provides automatic gain control that is relatively stable because transient data do not necessarily result in gain level changes. The simplicity of the algorithm processed by the invention makes hardware implementation feasible. These and other advantages of the invention will become more apparent upon review of the accompanying drawings and specification, including the claims.